The present invention relates to rocket engine injectors and ignition systems, and more particularly the present invention relates to non-hypergolic propellant injectors and ignition systems.
In a typical liquid propellant rocket engine, bi-propellant injection elements are used to facilitate the injection, distribution, mixing and combustion of an oxidizer and a fuel in a combustion chamber. In a large rocket engine, hundreds of injector elements may be present with a large ignition system assembly (or spark torch assembly) located in the center of the injector element array. The large ignition assembly can ignite the propellants by creating a standing flame or torch, like a “pilot light”, that is used to initiate combustion within the combustion chamber. This large ignition assembly utilizes its own dedicated propellant mixture to create and maintain the “pilot light”, and those dedicated propellant mixtures have significant differences from the propellant mixtures used to provide engine thrust. The need for dedicated “pilot light” propellant supplies complicates engine design. The use of large igniter assemblies also leads to performance losses due to the off-condition mixing of the dedicated propellants used to create the “pilot light” (i.e., due to use of a different mixture ratio than an optimum thrust performance mixture ratio). Moreover, large “pilot light” ignition assemblies are bulky in terms of both size and mass, which makes them less desirable for use with smaller rocket engines.
There are also known spark ignition systems for providing ignition sparks within a reaction zone in the combustion chamber. However, such systems present difficulties in fabricating system components and pose problems with component degradation during use. For instance, special injection orifices and manifolds are required to direct fuel and oxidizer to create an easily ignited mixture of propellants at the exposed electrodes. Direct spark ignition systems through an injector faceplate can also add weight, increase design complexity, and typically operate at off-optimum mixture ratios (usually at fuel-rich ratios) to preclude thermal damage to the electrodes, but which lower overall combustion performance.
Smaller rocket engines, such as positioning thruster engines, have historically used hypergolic propellants (i.e., propellants that spontaneously ignite when combined). However, it is desired to develop rocket engines that utilize non-hypergolic propellants.
The present invention provides a non-hypergolic propellant injection and ignition system that is suitable for use with relatively small rocket engines.